Cathode ray tube



1937- I E. DREWANZ ET AL 2,089,692

CATHODE RAY TUBE Filed Nov. 28, 1932 Inventors: Er'win Drewanz, ErnstBr-iiche, by M64 Their" Attorney.

Patented Aug. 10, 1937 CATHODE RAY TUBE Erwin Drewanz, Berlin,

and Ernst Briiehe, Berlin- Reinickendorf-Ost, Germany, assignors toGeneral Electric Company, a corporation of New York 11 (llairns.

When using electron tubes for sound recording and especially for soundpictures, it is advantageous to have the image produced by the electronrays on the stream, extend to the greatest possible distance. When thefluorescent spot is elongated in this manner and suitably controlled,the screen presents narrow lines of light which vary accurately inintensity according to the microphone current. When a film is moved pastthe end of the cathode-ray tube, these narrow lines cause correspondinglines to appear on the film and due to their extreme narrowness,production of sound from the film will be a faithful reproduction of theoriginal sound propagated into the microphone. The accuracy with whichthis reproduction is obtained depends, in part,

on the degree of narrowness of the light lines.

When electrons are emanated by a filament, it is usual to focus thecathode-rays by an elec- 0 trically charged cylinder of circularconfiguration in order to obtain maximum focusing eifect. The cathoderaystream in emerging from the cylinder or other focusing device has acircular configuration under these conditions and the problem presentsitself of changing the shape of the cathode-rays from that of a circleto a line, as narrow as possible. For this purpose, various arrangementshave been proposed, among which are those of a control grid having aspecial shape or the use of special diaphragms. In general, these priorarrangements have not given satisfactory results in that the fluorescentline produced has either been not sufiiciently narrow or else has losttoo high a percentage of its intensity or brightness during theconversion stage.

An object of the present invention is to provide a practical means forproducing a narrow fiuorescent line without substantial loss of lightintensity. This object is attained in brief by the use of magnetic orelectrostatic fields, generically termed electric fields which areproduced in the space between the anode and the screen by a suitablestructure. The effect of the magnetic or electrostatic field on thecathode-ray stream,

regardless of its original configuration, is to compress the electronbeam into a narrow strip or line.

When using a magnetic field for this purpose,

the field may advantageously be obtained from permanent magnets or ifdesired, from electromagnets excited by direct current. The magnets arepreferably arranged on either side of the tube so as to constitute afour-pole system having the poles of one magnet face the opposite polesof the other magnet. The magnet assembly is arranged with respect to thetube in such a manner that the electron beam passes perpendicularlythrough the center of the four-pole system. In other words, the magnetsare disposed equidistantly on either side of the envelope and arrangedperpendicularly thereto. It is found that under these conditions anarrow fiuoresoent light strip is produced, the brightness of which canbe changed in the usual manner by means of an electrostatic controlmember. The fluorescent strip can be made extremely narrow by regulatingthe distance of the magnets from the envelope and the intensity of themagnetic field. The length of the strip may be shortened, if desired, asfor example, when recording on a narrow sound film, by a suitablespherical or cylindrical lens system. The magnet arrangement forcontrolling the shape of the electron beam offers a marked advantage inthat the spot can be readily adjusted into the optical axis of therecording system, by displacing the plane of the magnet structure withrespect to the plane containing the axis of the electron beam.

The electrostatic method of obtaining the narrow light strip also offerscertain advantages over the prior art technique, mostly from thestandpoint of ease and accuracy of spot control and greatereffectiveness with which the electron beam is condensed from a. circularconfiguration to that of a line.

Physical embodiments of the invention are shown in the drawing in whichFig. 1 shows a longitudinal section of a cathode-ray tube with themagnets placed in accordance with our invention; Figs. 2 and 3diagrammatically show various ways of applying the magnetic field; Fig.4 illustrates the use of an electrostatic or condenser field forpurposes stated hereinbefore, while Fig. 5 is an enlarged perspectiveview of the electric-field-producing member.

In Fig. 1, numeral I designates the envelope of a highly evacuated orgas-containing cathode ray tube provided with a cathode 2, an anode 3, afocusing cylinder 4 and a fluorescent screen 5 coated on the interior ofthe envelope. The cathode, as illustrated, is of the indirectly heatedtype coated with electron-emitting material, although it will beunderstood that the directly heated form may also be used, if desired.The control member 4 is suitably charged for focusing purposes and ispreferably positioned so as to surround the cathode, therebyconstraining the electrons to the longitudinal aperture 6 contained inthe anode. The tube may be filled with a suitable gas such as argon ormercury vapor at well-known pressures. When an electromotive force, forexample 800 volts, is applied across the anode 3 and cathode 2, acomparatively large fluorescent spot of a general circular shapenormally appears on the screen and the intensity of the spot may becontrolled by the potential applied to the cylinder 5, as is well knownin the art.

In accordance with our invention, this normally extensive fluorescentspot is converted or condensed into a narrow light strip by the use ofmagnets i, 8 which preferably are positioned exterior of the envelope ina plane intermediate the anode 3 and the screen 5, as shown. This planepreferably is perpendicular to the electron stream axis unless somespecial converging effeet is required. As shown in Figs. 2 and 3, themagnets are symmetrically disposed with respect to the tube envelope andtheir unlike poles face one another. The fluorescent spot, whichnormally is round as it emerges from the opening 6, spreading itself outas it strikes the screen, is now constrained into a lateral strip 9parallel to the faces of the magnets when the latter are arranged asshown in Fig. 2. When the poles of the magnets are reversed as indicatedin Fig.

3, the light strip is moved through an angle of 90 and is now parallelto the longitudinal axis of the magnets. While we have shown the use ofpermanent magnets for this purpose, it. is obvious that electromagnetsenergized by direct current may also be used.

Instead of using a magnetic field for contracting the fluorescent spotinto a narrow line, electrostatic fields may be employed for thispurpose. As shown in Figs. 4 and 5, these fields are convenientlyobtained from a rectangular box member l2 made in the form of a hollowmetal frame with its edges nearer the anode 3 flared outwardly, asshown. Within the box there is a center strip it of metal, insulatinglysecured to the upper and lower sides of the box. The metal box andcontained strip are rigidly mounted in any suitable manner within theenvelope and positioned intermediate the anode 3 and the fluorescentscreen 5. The box is positioned in alignment with the opening in theanode 3, as shown. Separate leading-in conductors M, l5 are taken fromthe box and the strip respectively, to the exterior of the tube. Whenproper potentials are applied to the box and the strip depending chieflyon. the dimensions of the box and the velocity of the cathode rays, therays leaving the anode 3 are changed from a circular configuration intoa narrow strip or line. As examples of suitable potentials which may beapplied for this purpose, the center strip may have substantially thesame potential as the anode 3, while the box and therefore the two sideportions thereof which extend in parallel planes to the center strip,may have a produced is determined by the width of the center strip,hence by the distance between the upper and the lower sides of the box.While we have shown the electrostatic control member for changing theconfiguration of the electron beam from a circle to a line asconstituting a peripherally complete box, it is obvious that one or moreof the sides of the box may be left open, depending on the precise shapeand thickness of the fluorescent spot desired. However, it is preferableto provide a complete box as 11- lustrated, in order to lend ruggednessand rigidity to the structure.

What we claim as new and desire to secure by Letters Patent of theUnited States. is:

1. An. electron discharge device comprising an envelope containing anelectron-emitting cathode, a fluorescent screen and an anode having anopening other than rectangular, said anode being positioned between thescreen and cathode, and electric means for changing the configuration ofthe electron beam as it leaves the anode into an extended rectangularshape as it strikes the screen.

2. An electron discharge device comprising an envelope containing anelectron-emitting cathode, a fluorescent screen and an anode having anopening other than rectangular, said anode being positioned between thescreen and cathode, and electric means for changing the configuration ofthe electron beam as it leaves the anode into an extended rectangularshape as it strikes the screen, said means including a device forproducing a magnetic field between the cathode and screen.

3. An electron discharge device comprising an envelope containing anelectron-emitting cathode, a fluorescent screen and an anode having anopening other than rectangular, said anode being positioned between thescreen and cathode, and electric means for changing the configuration ofthe electron beam as it leaves the anode into an extended rectangularshape as its strikes the screen, said means including a device forproducing an electrostatic field between the cathode and screen.

4. An electron discharge device comprising an envelope containing anelectron-emitting cathode, an anode having a substantially rounddischarge opening, a fluorescent screen, and electric means positionedbetween the anode and screen for changing the circular configuration ofthe electron beam as it leaves the anode into an extended rectangularshape as it strikes the screen.

5. An electron discharge device comprising an envelope containing anelectron-emitting cathode, an anode having a substantially rounddischarge opening, a fluorescent screen, and electrostatic meanspositioned between the anode and screen for changing the circularconfiguration of the electron beam as it leaves the anode into anextended rectangular shape as it strikes the screen.

6. An electron discharge device comprising an envelope containing anelectron-emitting cathode, an anode having a substantially rounddischarge opening, a fluorescent screen, and magnetic means positionedbetween the anode and screen for changing the circular configuration ofthe electron beam as it leaves the anode into an extended substantiallyrectangular shape as it strikes the screen.

'7. An electron discharge device comprising an envelope containing anelectron-emitting cathode, an anode having a substantially rounddischarge opening, a fluorescent screen, and. magnetic means positionedbetween the anode and screen for changing the circular configuration ofthe electron beam as it leaves the anode into an extended substantiallyrectangular shape as it strikes the screen, said means including a pairof magnets arranged on opposite sides of the envelope, the poles of onemagnet facing the opposite poles of the other magnet.

8. An electron discharge device comprising an envelope containing anelectron-emitting cathode, an anode having a substantially rounddischarge opening, a fluorescent screen, and electric means positionedbetween the anode and screen for changing the circular configuration ofthe electron beam as it leaves the anode into an extended substantiallyrectangular shape as it strikes the screen, said means including a metalstrip arranged in line with the electron stream passing between theanode and the screen and a pair of metal strips positioned on eitherside of the said strip, and means for applying a potential to saidstrips.

9. An electron discharge device comprising an envelope containing anelectron-emitting cathode, an anode having a substantially rounddischarge opening, a fluorescent screen, and electric means positionedbetween the anode and screen for changing the circular configuration ofthe electron beam as it leaves the anode into an extended substantiallyrectangular shape as it strikes the screen, said means including arectangularly shaped hollow metal member containing a metal striparranged in line with the electron stream passing between the anode andthe screen.

10. An electron discharge device comprising an envelope containing anelectron-emitting cathode, an anode having a substantially rounddischarge opening, a fluorescent screen, and means positioned betweenthe anode and screen for changing the configuration of the electron beamas it leaves the anode into an extended substantially rectangular shapeas it strikes the screen, said means including a rectangularly shapedhollow metal member, a metal strip insulatingly supported within themember, said strip and member being arranged in line with the electronstream passing between the anode and screen, said strip adapted to becharged to a potential approximately equal to the anode potential.

11. An electron discharge device comprising an envelope containing anelectron-emitting cathode, an anode having a substantially rounddischarge opening, a fluorescent screen, and means positioned betweenthe anode and screen for changing the configuration of the electron beamas it leaves the anode into an extended substantially rectangular shapeas it strikes the screen, said means including a rectangularly shapedhollow metal member, a metal strip insulatingly supported within themember, said strip and member being arranged in line with the electronstream passing between the anode and screen, said strip adapted to becharged to a potential approximately equal to the anode potential, andsaid member adapted to be charged to a potential less than anodepotential.

ERWIN DREWANZ. ERNST BRI'lCHE.

